1. Technical Field
The present invention relates to a voltage monitoring apparatus to determine whether or not each cell voltage is normal in a plural battery that connects a plurality of unit cells in series to output a required voltage.
2. Background Art
For example, an electric car or a hybrid vehicle has a high-voltage battery as a power source for driving a motor. Such a high-voltage battery connects a plurality of unit cells of a secondary battery (rechargeable battery) such as a nickel-hydrogen battery and a lithium battery in series to provide a high voltage.
Each unit cell of the secondary battery is charged with the same power and is discharged at the same power. Accordingly, if the unit cells differently deteriorate, the secondary battery will easily get an overcharge or overdischarge state. To prevent the overcharge or overdischarge state of the secondary battery, the charging state of each unit cell must be checked.
Previously, a plurality of unit cells (for example, fifty five unit cells) are divided into, for example, five blocks (namely, eleven unit cells per block) and the voltage of each block is measured in real time with a voltage detecting IC provided for each block, to monitor if the voltage is abnormal.
At this time, the voltage detecting IC measures the voltage of each of the unit cells (for example, 11 cells) contained in the block and converts a measured analog voltage signal into a digital signal with an A/D converter provided for the voltage detecting IC. The digitized measured voltage is compared with upper and lower thresholds of cell voltage, and if the measured voltage is equal to or greater than the upper threshold, it is determined to be overcharge. If the measured voltage is equal to or lower than the lower threshold, it is determined to be overdischarge. A related art is disclosed in, for example, Japanese Unexamined Patent Application Publication No. 2010-35337. Thereafter, the determination result is transmitted as a digital fail signal to a microcomputer on a low-voltage side, so that the microcomputer may recognize the cell voltage abnormality.